- The deadly H5N1 bird flu strain that has been plaguing
southeast Asia appears to be evolving in a way that may signal a greater
threat of a human flu pandemic, according to a World Health Organization
report.
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- Human cases of avian influenza in northern Vietnam in
2005 are showing an epidemiological pattern and virological features which
differ from those seen in the 2004 cases. They also differ from those currently
seen in human cases in southern Vietnam and other Asian countries.
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- In particular, though not yet proven, the differences
indicate the virus may have already been transmitted from human-to-human,
a worrying prospect. It also suggests the viral strain in northern Vietnam
may be more infectious but less virulent than elsewhere, i.e. more easily
spread but less likely to cause death in sufferers.
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- "While the implications of these epidemiological
and virological findings are not fully clear, they demonstrate that the
viruses are continuing to evolve and pose a continuing and potentially
growing pandemic threat," says the WHO report on influenza A/H5N1
in humans in Asia. The report is based on its consultation meeting of experts
in Manila, Philippines on 6 and 7 May.
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- The great fear is that bird flu could hybridise with
human influenza or evolve to create a deadly and easily transmissible pandemic
strain that could sweep across the globe, killing millions.
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- "Things are getting more and more worrisome,"
says flu expert John Oxford, at Queen Mary University of London, UK. "It
does look as though the virus is moving towards being less virulent but
more infectious ñ if that's the way it's going, that's not good
news at all." Symptomless cases
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- The WHO document notes that while 83% of human cases
in southern Vietnam die, and 71% of cases in Thailand in 2004. In northern
Vietnam, the strain is felling 34% of sufferers, though that would still
be devastating if millions of people became infected.
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- Furthermore, three cases of symptomless infections have
also been seen in people who had close contact with confirmed cases in
Vietnam "suggesting that milder H5N1 infections are occurring".
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- "A virus with a mortality rate of 70% is never going
to get very far," says Oxford, as too many hosts die before infecting
large numbers of other people. But he believes that if the virus really
has changed in virulence, human-to-human transmission may be the next step.
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- Other evidence pointing to a change in the virus's nature
includes more clusters of human cases in north Vietnam compared with the
south. The ages of victims has also changed in northern Vietnam, with the
average age rising from 17 in 2004 to 31 in 2005. The range of ages affected
is also much wider, from babies to people over 80.
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- Lab observations indicate the virus has changed. Specific
gene changes have been pinpointed in the Vietnam strains from 2005, although
it is unclear what their significance is. Crippled virus
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- Analysis also revealed that drug resistance to the flu
drug oseltamivir had partially evolved in one patient treated with the
medicine. "The community emergence and spread of viruses resistant
to oseltamivir, if it were to occur, would have significant implications
for prevention and control," warns the document.
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- However, Oxford believes this is less concerning than
the other changes. He says full drug resistance in human flu strains somewhat
"cripples" their effectiveness in spreading.
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- The WHO recommends that countries ramp up their flu pandemic
preparedness plans, stockpile antiviral drugs, and explore ways of making
human H5N1 vaccine available to affected Asian countries before a pandemic
develops.
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- Though the situation is concerning, it "still hasn't
exploded", notes Oxford. "We have more time to prepare ourselves,"
he told New Scientist. But countries without a pandemic preparedness plan
"should wake up", he says, "otherwise it'll be like a tsunami
wave and we'll all be caught in it".
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- © Copyright Reed Business Information Ltd.
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- http://www.newscientist.com/article.ns?id=dn7402
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